The Effect of Induced Anisometropia nn Binocular Visual Function

Abstract

Background

To determine the effect of experimentally induced anisometropia on binocular function in healthy adults as a means of assessing the likely effects of uncorrected anisometropia on binocular visual development in childhood.

Design

Patients and Methods

A total of 30 healthy adults aged between 18-35 years and free of ocular disease participated in the study. One to five diopter (D) of unilateral hypermetropia and myopia was induced in each eye in ID increments. Fusion was assessed with the Worth-Four Dot test for distance (WFDT) and near and Bagolini’s lenses (BL); stereopsis with the TNO test, bifoveal fusion with the four-prism diopter base-out test (4PDBOT) and aniseikoniawith charts.

Results

All subjects showed a decline in binocular function with increasing levels of anisometropia. Significantly increasing foveal suppression as evident on the WFDT and BL, with all subjects definitely suppressing at +3 Danisometropia. Aniseikonia was altered by 2% per 1 D anisometropic Induction. Proportion of cases with monofixation significantly increased upto 3D (p<0.05). Stereopsis decreased in proportion to the degree of anisometropia. Three diopters of anisometropia, regardless of type, produced a marked reduction of stereoacuity in all patients.

Conclusions

Relatively low degrees of spherical anisometropia (as small as 1D) causes significant abnormalities in high-grade binocular function in adults. The potential amblyogenic effects of even small uncorrected anisometropia on binocularity in children require further investigation, and should be considered in developing guidelines for the empiric correction of refractive errors.